U.S. patent application number 11/454019 was filed with the patent office on 2007-12-20 for apparatus and method for downhole dynamics measurements.
This patent application is currently assigned to PathFinder Energy Services, Inc.. Invention is credited to Junichi Sugiura.
Application Number | 20070289373 11/454019 |
Document ID | / |
Family ID | 38860276 |
Filed Date | 2007-12-20 |
United States Patent
Application |
20070289373 |
Kind Code |
A1 |
Sugiura; Junichi |
December 20, 2007 |
Apparatus and method for downhole dynamics measurements
Abstract
Aspects of this invention include a rotary steerable steering
tool having a sensor arrangement for measuring downhole dynamic
conditions. Rotary steerable tools in accordance with this
invention include a rotation rate measurement device disposed to
measure a difference in rotation rates between a drive shaft and an
outer, substantially non-rotating housing. A controller is
configured to determine a stick/slip parameter from the rotation
rate measurements. Exemplary embodiments may also optionally
include a tri-axial accelerometer arrangement deployed in the
housing for measuring lateral vibrations and bit bounce. Downhole
measurement of stick/slip and other vibration components during
drilling advantageously enables corrective measures to be
implemented when dangerous dynamic conditions are encountered.
Inventors: |
Sugiura; Junichi; (Houston,
TX) |
Correspondence
Address: |
W-H ENERGY SERVICES, INC.
2000 W. Sam Houston Pkwy. S, SUITE 500
HOUSTON
TX
77042
US
|
Assignee: |
PathFinder Energy Services,
Inc.
Houston
TX
|
Family ID: |
38860276 |
Appl. No.: |
11/454019 |
Filed: |
June 15, 2006 |
Current U.S.
Class: |
73/152.46 ;
73/152.01 |
Current CPC
Class: |
E21B 7/062 20130101;
E21B 45/00 20130101; E21B 47/024 20130101; E21B 44/00 20130101;
E21B 47/00 20130101; E21B 47/12 20130101 |
Class at
Publication: |
73/152.46 ;
73/152.01 |
International
Class: |
E21B 47/00 20060101
E21B047/00 |
Claims
1. A rotary steerable tool configured to operate in a borehole, the
rotary steerable tool comprising: a shaft; a housing deployed about
the shaft, the shaft disposed to rotate substantially freely in the
housing; a rotation rate measurement device disposed to measure a
rotation rate of the shaft relative to the housing, the rotation
rate measurement device including at least one sensor and at least
one marker, the sensor disposed to send an electrical pulse to a
controller each time one of the markers and the sensor rotate past
one another; and the controller configured to calculate a
stick/slip parameter from said electric pulses.
2. The rotary steerable tool of claim 1, wherein the controller is
configured to calculate the stick/slip parameter according to an
equation selected from the group consisting of: S S = R P M MAX - R
P M MIN .apprxeq. R P M MAX ; ##EQU00008## S S N = R P M MAX - R P
M MIN R P M AVE .apprxeq. R P M MAX R P M AVE ; ##EQU00008.2## S S
= N MAX - N MIN .apprxeq. N MAX ; ##EQU00008.3## S S N = N MAX - N
MIN N AVE .apprxeq. N MAX N AVE ; ##EQU00008.4## S S = ( R P M ( t
) ) t = R P M ( t ) - R P M ( t - 1 ) ; and ##EQU00008.5## S S N =
( R P M ( t ) ) t R P M AVE = R P M ( t ) - R P M ( t - 1 ) R P M
AVE ; ##EQU00008.6## where SSN represents the stick/slip parameter
normalized, SS represents the stick/slip parameter, RPM.sub.MAX,
RPM.sub.MIN, and RPM.sub.AVE represent a maximum instantaneous
rotation rate, a minimum instantaneous rotation rate, and an
average rotation rate of the shaft, respectively, N.sub.MAX and
N.sub.MIN represent maximum and minimum numbers of the electrical
pulses, N.sub.AVE represents an average number of the electrical
pulses, d(RPM(t))/dt represents the differential of an
instantaneous rotation rate with time, and RPM(t) and RPM(t-1)
represent instantaneous rotation rates of the shaft in sequential
time periods.
3. The rotary steerable tool of claim 1, wherein the controller is
further configured to calculate instantaneous and average rotation
rates of the shaft relative to the housing from said electrical
pulses.
4. The rotary steerable tool of claim 1, wherein the controller is
further configured to calculate the rotation rate of the shaft
according to at least one equation from the group consisting of: R
P M = N .DELTA. t 60 n ; and R P M = 60 m n .delta. t ;
##EQU00009## where RPM represents the rotation rate of the shaft in
revolutions per minute, N represents a number of electrical pulses
in a predetermined time period, .DELTA.t represents a length of
time of the predetermined time period in seconds, n represents a
number of markers utilized in the rotation rate measurement device,
and .delta.t represents a time interval between the m electrical
pulses in seconds.
5. The rotary steerable tool of claim 1, wherein the rotation rate
measurement device comprises a Hall-effect sensor deployed in the
housing and a plurality of magnetic markers deployed on the
shaft.
6. The rotary steerable tool of claim 1, further comprising: a
tri-axial arrangement of accelerometers deployed in the housing,
one of the accelerometers substantially aligned with a longitudinal
axis of the rotary steerable tool, the accelerometers disposed to
measure tri-axial acceleration components of the housing.
7. The rotary steerable tool of claim 6, wherein the controller is
further configured to determine a bit bounce parameter and a
lateral vibration parameter from said measured tri-axial
acceleration components.
8. The rotary steerable tool of claim 7, wherein the controller is
further configured to determine borehole inclination and gravity
tool face from said measured tri-axial acceleration components.
9. The rotary steerable tool of claim 7, wherein the controller is
further configured to determine (i) the bit bounce parameter from a
difference between instantaneous and average axial acceleration
components and (ii) the lateral vibration parameter from a
difference between instantaneous and average cross axial
acceleration components.
10. A rotary steerable tool configured to operate in a borehole,
the rotary steerable tool comprising: a shaft; a housing deployed
about the shaft, the shaft disposed to rotate substantially freely
in the housing; a rotation rate measurement device disposed to
measure a rotation rate of the shaft relative to the housing, the
rotation rate measurement device including at least one sensor and
a plurality of markers, the sensor disposed to send an electrical
pulse to a controller each time one of the markers and the sensor
rotate past one another; a tri-axial accelerometer set deployed in
the housing, the accelerometer set disposed to measure acceleration
of the housing; and the controller configured to determine (i)
instantaneous and average rotation rates of the shaft from said
electrical pulses, (ii) a stick/slip parameter from said
instantaneous rotation rates, (iii) instantaneous and average
tri-axial acceleration components from said accelerometer
measurements, (iv) borehole inclination and gravity tool face from
the average tri-axial acceleration components, and (v) bit bounce
and lateral vibration parameters from the instantaneous tri-axial
acceleration components.
11. The rotary steerable tool of claim 10, wherein the rotation
rate measurement device comprises a Hall-effect sensor deployed in
the housing and a plurality of magnetic markers deployed on the
shaft.
12. The rotary steerable tool of claim 10, further comprising:
downhole memory suitable for storing the following parameters at
predetermined time intervals during drilling; (i) the instantaneous
and average rotation rates of the shaft, (ii) the stick/slip
parameter, (iii) the instantaneous and average tri-axial
acceleration components, (iv) borehole inclination and gravity tool
face, and (v) the bit bounce and lateral vibration parameters.
13. The rotary steerable tool of claim 10, wherein the controller
is in electronic communication with a telemetry device configured
to telemeter selected ones of the stick/slip parameter, the bit
bounce parameter, and the lateral vibration parameter to a surface
location.
14. The rotary steerable tool of claim 10, wherein: the controller
is configured to calculate the stick/slip parameter according to at
least one equation selected from the group consisting of: S S = R P
M MAX - R P M MIN .apprxeq. R P M MAX ; ##EQU00010## S S N = R P M
MAX - R P M MIN R P M AVE .apprxeq. R P M MAX R P M AVE ;
##EQU00010.2## S S = N MAX - N MIN .apprxeq. N MAX ; ##EQU00010.3##
S S N = N MAX - N MIN N AVE .apprxeq. N MAX N AVE ; ##EQU00010.4##
S S = ( R P M ( t ) ) t = R P M ( t ) - R P M ( t - 1 ) ; and
##EQU00010.5## S S N = ( R P M ( t ) ) t R P M AVE = R P M ( t ) -
R P M ( t - 1 ) R P M AVE ; ##EQU00010.6## where SSN represents the
stick/slip parameter normalized, SS represents the stick/slip
parameter, RPM.sub.MAX, RPM.sub.MIN, and RPM.sub.AVE represent a
maximum instantaneous rotation rate, a minimum instantaneous
rotation rate, and an average rotation rate of the shaft,
respectively, N.sub.MAX and N.sub.MIN represent maximum and minimum
numbers of the electrical pulses, N.sub.AVE represents an average
number of the electrical pulses, d(RPM(t))/dt represents the
differential of an instantaneous rotation rate with time, and
RPM(t) and RPM(t-1) represent instantaneous rotation rates of the
shaft in sequential time periods.
15. The rotary steerable tool of claim 10, wherein: the controller
is configured to calculate the bit bounce and lateral vibration
parameters according to at least one equation selected from the
group consisting of: T V = G i - G iAVE ; ##EQU00011## T V = G iMAX
- G iMIN ; ##EQU00011.2## T V = G iMAX - G iAVE ; ##EQU00011.3## T
V = G iMIN - G iAVE ; and ##EQU00011.4## T V = ( G i ( t ) ) t = G
i ( t ) - G i ( t - 1 ) ; ##EQU00011.5## where TV represents one of
the bit bounce and lateral vibration parameters, G.sub.i represents
an instantaneous acceleration component along one of x, y, and
axes, G.sub.iAvE represents an average acceleration component,
G.sub.iMAX and G.sub.iMIN represent maximum and minimum
instantaneous acceleration components, and G.sub.i(t) and
G.sub.i(t-1) represent sequential instantaneous acceleration
components.
16. A method for determining a stick/slip parameter downhole during
drilling of subterranean borehole, the method comprising: (a)
rotating a string of tools in a borehole, the string of tools
including a rotary steerable tool and a drill bit rotationally
coupled with a drill string, the rotary steerable tool including a
shaft disposed to rotate substantially freely in a housing, the
rotary steerable tool further including a rotation rate measurement
device disposed to measure a rotation rate of the shaft relative to
the housing, the rotation rate measurement device having at least
one sensor and a plurality of markers, the sensor disposed to send
an electrical pulse to a controller each time one of the markers
and the sensor rotate past one another; and (b) processing said
electrical pulses to determine the stick/slip parameter.
17. The method of claim 16, wherein (b) further comprises: (i)
processing the electrical pulses to determine a plurality of
instantaneous rotation rates of the shaft; and (ii) processing the
plurality of instantaneous rotation rates to determine the
stick/slip parameter.
18. The method of claim 16, wherein (b) further comprises: (i)
processing the electrical pulses to determine a plurality of
instantaneous rotation rates of the shaft and an average rotation
rate of the shaft; and (ii) processing the plurality of
instantaneous rotation rates and the average rotation rate to
determine the stick/slip parameter.
19. The method of claim 16, wherein (b) further comprises: (i)
counting a number of electrical pulses in each of a plurality of
time intervals; (ii) determining a maximum number of electrical
pulses in the plurality of time intervals; and (iii) processing the
maximum number of electrical pulses to determine the stick/slip
parameter.
20. The method of claim 19, wherein: (ii) further comprises
determining a minimum number of electrical pulses in the plurality
of time intervals and an average number of electrical pulses in the
plurality of time intervals; and (iii) further comprises processing
the maximum number, the minimum number, and to the average number
of electrical pulses to determine the stick/slip parameter.
21. The method of claim 16, further comprising: (c) telemetering
said stick/slip parameter to a surface location.
22. The method of claim 16, wherein the stick/slip parameter is
determined in (b) according to at least one equation of the group
consisting of: S S = R P M MAX - R P M MIN .apprxeq. R P M MAX ;
##EQU00012## S S N = R P M MAX - R P M MIN R P M AVE .apprxeq. R P
M MAX R P M AVE ; ##EQU00012.2## S S = N MAX - N MIN .apprxeq. N
MAX ; ##EQU00012.3## S S N = N MAX - N MIN N AVE .apprxeq. N MAX N
AVE ; ##EQU00012.4## S S = ( R P M ( t ) ) t = R P M ( t ) - R P M
( t - 1 ) ; and ##EQU00012.5## S S N = ( R P M ( t ) ) t R P M AVE
= R P M ( t ) - R P M ( t - 1 ) R P M AVE ; ##EQU00012.6## where
SSN represents the stick/slip parameter normalized, SS represents
the stick/slip parameter, RPM.sub.MAX, RPM.sub.MIN, and RPM.sub.AVE
represent a maximum instantaneous rotation rate, a minimum
instantaneous rotation rate, and an average rotation rate of the
shaft, respectively, N.sub.MAX and N.sub.MIN represent maximum and
minimum numbers of the electrical pulses, N.sub.AVE represents an
average number of the electrical pulses, d(RPM(t))/dt represents
the differential of an instantaneous rotation rate with time, and
RPM(t) and RPM(t-1) represent instantaneous rotation rates of the
shaft in sequential time periods.
23. The method of claim 16, wherein: the rotary steerable tool
further includes a tri-axial arrangement of accelerometers deployed
in the housing, one of the accelerometers substantially aligned
with a longitudinal axis of the rotary steerable tool; and the
method further comprises: (c) causing the accelerometers to measure
tri-axial acceleration components of the housing; and (d)
processing said tri-axial acceleration components measured in (c)
to determine at least one of a bit bounce parameter and a lateral
vibration parameter.
24. The method of claim 23, wherein (d) further comprises: (i)
processing a difference between instantaneous and average axial
acceleration components measured in (c) to determine the bit bounce
parameter; and (ii) processing a difference between instantaneous
and average cross axial acceleration components measured in (c) to
determine the lateral vibration parameter.
25. The method of claim 23, further comprising: (e) processing said
tri-axial acceleration components measured in (c) to determine
borehole inclination and gravity tool face.
26. The method of claim 23, wherein the bit bounce parameter and
the lateral vibration parameter are determined in (d) according to
at least one equation selected from the group consisting of: T V =
G i - G iAVE ##EQU00013## T V = G iMAX - G iMIN ##EQU00013.2## T V
= G iMAX - G iAVE ; ##EQU00013.3## T V = G iMIN - G iAVE ; and
##EQU00013.4## T V = ( G i ( t ) ) t = G i ( t ) - G i ( t - 1 )
##EQU00013.5## where TV represents one of the bit bounce and
lateral vibration parameters, G.sub.i represents an instantaneous
acceleration component along one of x, y, and axes, G.sub.iAVE
represents an average acceleration component, G.sub.iMAX and
G.sub.iMIN represent maximum and minimum instantaneous acceleration
components, and G.sub.i(t) and G.sub.i(t-1) represent sequential
instantaneous acceleration components.
27. The method of claim 23, further comprising: (e) telemetering
the stick/slip parameter, the bit bounce parameter, and the lateral
vibration parameter to a surface location.
28. A method for determining downhole dynamics parameters downhole
during drilling of subterranean borehole, the method comprising:
(a) rotating a string of tools in a borehole, the string of tools
including a rotary steerable tool and a drill bit rotationally
coupled with a drill string, the rotary steerable tool including a
shaft disposed to rotate substantially freely in a housing, the
rotary steerable tool further including a rotation rate measurement
device disposed to measure a rotation rate of the shaft relative to
the housing, the rotation rate measurement device having at least
one sensor and a plurality of markers, the sensor disposed to send
an electrical pulse to a controller each time one of the markers
and the sensor rotate past one another, the rotary steerable tool
further including a tri-axial accelerometer set deployed in the
housing; (b) processing said electrical pulses to determine
instantaneous and average rotation rates of the shaft; (c)
processing the instantaneous rotation rate to determine a
stick/slip parameter; (d) causing the accelerometers to measure
tri-axial acceleration components of the housing; and (e)
processing the tri-axial acceleration components measured in (d) to
determine a bit bounce parameter and a lateral vibration
parameter.
29. The method of claim 28, wherein the stick/slip parameter is
determined in (c) according to at least one equation of the group
consisting of: S S = R P M MAX - R P M MIN .apprxeq. R P M MAX ;
##EQU00014## S S N = R P M MAX - R P M MIN R P M AVE .apprxeq. R P
M MAX R P M AVE ; ##EQU00014.2## S S = N MAX - N MIN .apprxeq. N
MAX ; ##EQU00014.3## S S N = N MAX - N MIN N AVE .apprxeq. N MAX N
AVE ; ##EQU00014.4## S S = ( R P M ( t ) ) t = R P M ( t ) - R P M
( t - 1 ) ; and ##EQU00014.5## S S N = ( R P M ( t ) ) t R P M AVE
= R P M ( t ) - R P M ( t - 1 ) R P M AVE ; ##EQU00014.6## where
SSN represents the stick/slip parameter normalized, SS represents
the stick/slip parameter, RPM.sub.MAX, RPM.sub.MIN, and RPM.sub.AVE
represent a maximum instantaneous rotation rate, a minimum
instantaneous rotation rate, and an average rotation rate of the
shaft, respectively, N.sub.MAX and N.sub.MIN represent maximum and
minimum numbers of the electrical pulses, N.sub.AVE represents an
average number of the electrical pulses, d(RPM(t))/dt represents
the differential of an instantaneous rotation rate with time, and
RPM(t) and RPM(t-1) represent instantaneous rotation rates of the
shaft in sequential time periods.
30. The method of claim 28, wherein the bit bounce parameter and
the lateral vibration parameter are determined in (e) according to
at least one equation selected from the group consisting of: T V =
G i - G iAVE ##EQU00015## T V = G iMAX - G iMIN ##EQU00015.2## T V
= G iMAX - G iAVE ; ##EQU00015.3## T V = G iMIN - G iAVE ; and
##EQU00015.4## T V = ( G i ( t ) ) t = G i ( t ) - G i ( t - 1 )
##EQU00015.5## where TV represents one of the bit bounce and
lateral vibration parameters, G.sub.i represents an instantaneous
acceleration component along one of x, y, and axes, G.sub.iAVE
represents an average acceleration component, G.sub.iMAX and
G.sub.iMIN represent maximum and minimum instantaneous acceleration
components, and G.sub.i(t) and G.sub.i(t-1) represent sequential
instantaneous acceleration components.
31. The method of claim 28, further comprising: (f) telemetering
the stick/slip parameter, the bit bounce parameter, and the lateral
vibration parameter to a surface location.
Description
RELATED APPLICATIONS
[0001] None.
FIELD OF THE INVENTION
[0002] The present invention relates generally to downhole tools,
for example, including three-dimensional rotary steerable tools
(3DRS ). More particularly, embodiments of this invention relate to
an apparatus and method for measuring the dynamic conditions of a
rotary steerable tool, and in particular, a method and apparatus
for measuring stick/slip conditions.
BACKGROUND OF THE INVENTION
[0003] Directional control has become increasingly important in the
drilling of subterranean oil and gas wells, for example, to more
fully exploit hydrocarbon reservoirs. Two-dimensional and
three-dimensional rotary steerable tools are used in many drilling
applications to control the direction of drilling. Such steering
tools commonly include a plurality of force application members
(also referred to herein as blades) that may be independently
extended out from and retracted into a housing. The blades are
disposed to extend outward from the housing into contact with the
borehole wall and to thereby displace the housing from the
centerline of a borehole during drilling. The housing is typically
deployed about a shaft, which is coupled to the drill string and
disposed to transfer weight and torque from the surface (or from a
mud motor) through the steering tool to the drill bit assembly.
[0004] It is well known in the art that severe dynamic conditions
are often encountered during drilling. Commonly encountered dynamic
conditions include, for example, bit bounce, lateral shock and
vibration, and stick/slip. Bit bounce includes axial vibration of
the drill string, often resulting in temporary lift off of the
drill bit from the formation ("bouncing" of the drill bit off the
bottom of the borehole). Bit bounce is known to reduce the rate of
penetration (ROP) during drilling, cause excessive fatigue damage
to BHA components, and may even damage the well in extreme
conditions. Lateral vibrations are those which are transverse to
the axis of the drill string. Such lateral vibrations are commonly
recognized as the leading cause of drill string and BHA failures
and may be caused, for example, by bit whirl and/or the use of
unbalanced drill string components. Stick/slip refers to a
torsional vibration induced by friction between drill string
components and the borehole wall. Stick/slip is known to produce
instantaneous drill string rotation speeds many times that of the
nominal rotation speed of the table. In stick/slip conditions a
portion of the drill string or bit sticks to the borehole wall due
to frictional forces often causing the drill string to temporarily
stop rotating. Meanwhile, the rotary table continues to turn
resulting in an accumulation of torsional energy in the drill
string. When the torsional energy exceeds the static friction
between the drill string and the borehole, the energy is released
suddenly in a rapid burst of drill string rotation. Instantaneous
downhole rotation rotates have been reported to exceed four times
that of the rotary table. Stick/slip is known to cause severe
damage to downhole tools, as well as connection fatigue, and excess
wear to the drill bit and near-bit stabilizer blades. Such wear
commonly results in reduced ROP and loss of steerability in
deviated boreholes. These harmful dynamic conditions not only cause
premature failure and excessive wear of the drilling components,
but also often result in costly trips (tripping-in and tripping-out
of the borehole) due to unexpected tool failures and wear.
Furthermore, there is a trend in the industry towards drilling
deeper, smaller diameter wells where stick/slip becomes
increasingly problematic. Problems associated with premature tool
failure and wear are exacerbated (and more expensive) in such
wells.
[0005] The above-described downhole dynamic conditions are known to
be influenced by drilling conditions. By controlling such drilling
conditions an operator can sometimes mitigate against damaging
dynamic conditions. For example, bit bounce and lateral vibration
conditions can sometimes be overcome by reducing both the weight on
bit and the drill string rotation rate. Stick/slip conditions can
often be overcome via increasing the drill string rotation rate and
reducing weight on bit. The use of less aggressive drill bits also
tends to reduce bit bounce, lateral vibrations, and stick/slip in
many types of formations. The use of stiffer drill string
components is further known to sometimes reduce stick/slip. While
the damaging dynamic conditions may often be mitigated as described
above, reliable measurement and identification of such dynamic
conditions can be problematic. For example, lateral vibration and
stick/slip conditions are not easily quantified by surface
measurements. In fact, such dynamic conditions are sometimes not
even detectable at the surface, especially at vibration frequencies
above about 5 hertz.
[0006] Downhole dynamics measurement systems have been known in the
art for at least 15 years. For example, U.S. Pat. No. 4,958,125 to
Jardine et al discloses an accelerometer-based method for measuring
the centripetal acceleration of a drill string in a borehole, and
thereby determining instantaneous rotation rates of the drill
string. More recently, U.S. Pat. No. 6,518,756 to Morys et al
discloses a system and apparatus for determining the lateral
velocity of a drill string within a borehole. While these, and
other known systems and methods, may be serviceable in certain
applications, there is yet need for further improvement. For
example, the above-described methods each require at least four
accelerometers deployed about the periphery of the drill string
(Morys et al also requires the deployment of two additional
magnetometers). The use of such dedicated sensors tends to increase
costs and expend valuable BHA real estate (e.g., via the
introduction of a dedicated sub). Also, such dedicated sensors tend
to increase power consumption and component counts and, therefore,
the complexity of MWD, LWD, and directional drilling tools, and
thus tend to reduce reliability of the system. Moreover, dedicated
sensors must typically be deployed a significant distance above the
drill bit.
[0007] Therefore there exists a need for an improved apparatus and
method for making downhole dynamics measurements. In particular,
there exists a need for a rotary steerable deployment of such a
dynamics measurement system and method.
SUMMARY OF THE INVENTION
[0008] The present invention addresses one or more of the
above-described drawbacks of prior art tools and methods. Aspects
of this invention include a rotary steerable steering tool having a
sensor arrangement for measuring downhole dynamic conditions. In
one exemplary embodiment, a rotary steerable tool in accordance
with this invention includes a rotation rate sensor disposed to
measure a difference in rotation rates between a drive shaft and an
outer, substantially non-rotating housing. The rotation rate sensor
may include, for example, a Hall-effect sensor. The rotary
steerable tool may also optionally include a tri-axial
accelerometer arrangement deployed in the housing for measuring
lateral vibrations and bit bounce. Stick/slip conditions may be
determined at the steering tool, for example, by comparing
instantaneous and time-averaged rotation rate measurements. Drill
string vibration may be determined via lateral and axial
acceleration measurements.
[0009] Exemplary embodiments of the present invention may
advantageously provide several technical advantages. For example,
in one exemplary embodiment, real-time, downhole measurement of
stick/slip and other vibration components during drilling enables
corrective measures to be implemented when dangerous dynamic
conditions are encountered. Moreover, exemplary method embodiments
of this invention advantageously utilize existing rotation rate and
accelerometer sensors deployed in a rotary steerable housing. This
enables simultaneous determination of downhole dynamics,
inclination, tool face, and average drill string rotation, which
allows for increased reliability of the sensor system by reducing
component counts.
[0010] In one aspect the present invention includes a rotary
steerable tool configured to operate in a borehole. The rotary
steerable tool includes a shaft and a housing deployed about the
shaft, the shaft disposed to rotate substantially freely in the
housing. The rotary steerable tool also includes a rotation rate
measurement device disposed to measure a rotation rate of the shaft
relative to the housing. The rotation rate measurement device
includes at least one sensor and at least one marker, the sensor
disposed to send an electrical pulse to a controller each time one
of the markers and the sensor rotate past one another, the
controller being configured to calculate a stick/slip parameter
from the electric pulses.
[0011] In another aspect this invention includes a rotary steerable
tool configured to operate in a borehole. The rotary steerable tool
includes a shaft and a housing deployed about the shaft, the shaft
being disposed to rotate substantially freely in the housing. The
rotary steerable tool also includes a rotation rate measurement
device disposed to measure a rotation rate of the shaft relative to
the housing. The rotation rate measurement device includes at least
one sensor and a plurality of markers, the sensor disposed to send
an electrical pulse to a controller each time one of the markers
and the sensor rotate past one another. The rotary steerable tool
further includes a tri-axial accelerometer set deployed in the
housing, the accelerometer set disposed to measure acceleration of
the housing. The controller is configured to determine (i)
instantaneous and average rotation rates of the shaft from the
electrical pulses, (ii) a stick/slip parameter from the
instantaneous rotation rates, (iii) instantaneous and average
tri-axial acceleration components from the accelerometer
measurements, (iv) borehole inclination and gravity tool face from
the average tri-axial acceleration components, and (v) bit bounce
and lateral vibration parameters from the instantaneous tri-axial
acceleration components.
[0012] In another aspect the present invention includes a method
for determining a stick/slip parameter downhole during drilling of
subterranean borehole. The method includes rotating a string of
tools in a borehole, the string of tools including a rotary
steerable tool and a drill bit rotationally coupled with a drill
string, the rotary steerable tool including a shaft disposed to
rotate substantially freely in a housing, the rotary steerable tool
further including a rotation rate measurement device disposed to
measure a rotation rate of the shaft relative to the housing, the
rotation rate measurement device having at least one sensor and a
plurality of markers, the sensor disposed to send an electrical
pulse to a controller each time one of the markers and the sensor
rotate past one another. The method further includes processing the
electrical pulses to determine the stick/slip parameter.
[0013] The foregoing has outlined rather broadly the features of
the present invention in order that the detailed description of the
invention that follows may be better understood. Additional
features and advantages of the invention will be described
hereinafter which form the subject of the claims of the invention.
It should be appreciated by those skilled in the art that the
conception and the specific embodiments disclosed may be readily
utilized as a basis for modifying or designing other methods,
structures, and encoding schemes for carrying out the same purposes
of the present invention. It should also be realized by those
skilled in the art that such equivalent constructions do not depart
from the spirit and scope of the invention as set forth in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] For a more complete understanding of the present invention,
and the advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawings,
in which:
[0015] FIG. 1 depicts a drilling rig on which exemplary embodiments
of the present invention may be deployed.
[0016] FIG. 2 is a perspective view of the steering tool shown on
FIG. 1.
[0017] FIG. 3 depicts, in cross section, a portion of the steering
tool shown on FIG. 2 showing one exemplary sensor arrangement in
accordance with this invention
[0018] FIG. 4 depicts one exemplary method embodiment of the
present invention in flowchart form.
[0019] FIG. 5 depicts, in cross section, another portion of the
steering tool shown on FIG. 2 showing another exemplary sensor
arrangement in accordance with this invention.
[0020] FIG. 6 depicts another exemplary method embodiment of the
present invention in flowchart form.
[0021] FIG. 7 depicts a block diagram of an exemplary control
circuit in accordance with the present invention.
DETAILED DESCRIPTION
[0022] Referring first to FIGS. 1, 2, 3, and 7, it will be
understood that features or aspects of the embodiments illustrated
may be shown from various views. Where such features or aspects are
common to particular views, they are labeled using the same
reference numeral. Thus, a feature or aspect labeled with a
particular reference numeral on one view in FIGS. 1, 2, 3, 5, and 7
may be described herein with respect to that reference numeral
shown on other views.
[0023] FIG. 1 illustrates a drilling rig 10 suitable for utilizing
exemplary rotary steerable tool and method embodiments of the
present invention. In the exemplary embodiment shown on FIG. 1, a
semisubmersible drilling platform 12 is positioned over an oil or
gas formation (not shown) disposed below the sea floor 16. A subsea
conduit 18 extends from deck 20 of platform 12 to a wellhead
installation 22. The platform may include a derrick 26 and a
hoisting apparatus 28 for raising and lowering the drill string 30,
which, as shown, extends into borehole 40 and includes a drill bit
32 and a directional drilling tool 100 (such as a three-dimensional
rotary steerable tool). In the exemplary embodiment shown, a rotary
steerable tool 100 includes one or more, usually three, blades 150
disposed to extend outward from the tool 100 and apply a lateral
force and/or displacement to the borehole wall 42. The extension of
the blades deflects the drill string 30 from the central axis of
the borehole 40, thereby changing the drilling direction. Exemplary
embodiments of rotary steerable tool 100 further include first and
second sensor arrangements 200 and 300, which may be utilized in
combination to measure downhole dynamics of the drill string 30.
Drill string 30 may further include a downhole drilling motor, a
mud pulse telemetry system, and one or more additional sensors,
such as LWD and/or MWD tools for sensing downhole characteristics
of the borehole and the surrounding formation. The invention is not
limited in these regards.
[0024] It will be understood by those of ordinary skill in the art
that methods and apparatuses in accordance with this invention are
not limited to use with a semisubmersible platform 12 as
illustrated in FIG. 1. This invention is equally well suited for
use with any kind of subterranean drilling operation, either
offshore or onshore.
[0025] Turning now to FIG. 2, one exemplary embodiment of rotary
steerable tool 100 from FIG. 1 is illustrated in perspective view.
In the exemplary embodiment shown, rotary steerable tool 100 is
substantially cylindrical and includes threaded ends 102 and 104
(threads not shown) for connecting with other bottom hole assembly
(BHA) components (e.g., connecting with the drill bit at end 104).
The rotary steerable tool 100 further includes a housing 110 and at
least one blade 150 deployed, for example, in a recess (not shown)
in the housing 110. Rotary steerable tool 100 further includes
hydraulics 130 and electronics 140 modules (also referred to herein
as control modules 130 and 140) deployed in the housing 110. In
general, the control modules 130 and 140 are configured for sensing
and controlling the relative positions of the blades 150 and may
include substantially any devices known to those of skill in the
art, such as those disclosed in U.S. Pat. No. 5,603,386 to Webster
or U.S. Pat. No. 6,427,783 to Krueger et al.
[0026] To steer (i.e., change the direction of drilling), one or
more of blades 150 are extended and exert a force against the
borehole wall. The rotary steerable tool 100 is moved away from the
center of the borehole by this operation, altering the drilling
path. It will be appreciated that the tool 100 may also be moved
back towards the borehole axis if it is already eccentered. To
facilitate controlled steering, the tool 100 is constructed so that
the housing 110, which houses the blades 150, remains stationary,
or substantially stationary, with respect to the borehole during
steering operations. The rotation rate of the housing is typically
less than 0.1 rpm during drilling, although the invention is not
limited in this regard. If the desired change in direction requires
moving the center of the rotary steerable tool 100 a certain
direction from the centerline of the borehole, this objective is
achieved by actuating one or more of the blades 150. By keeping the
blades 150 in a substantially fixed position with respect to the
circumference of the borehole (i.e., by preventing rotation of the
housing 110), it is possible to steer the tool without constantly
extending and retracting the blades 150. The housing 110,
therefore, is constructed in a rotationally non-fixed or floating
fashion.
[0027] In general, increasing the offset (i.e., increasing the
distance between the tool axis and the borehole axis) tends to
increase the curvature (dogleg severity) of the borehole upon
subsequent drilling. In the exemplary embodiment shown, rotary
steerable tool 100 includes near-bit stabilizer 120, and is
therefore configured for "point-the-bit" steering in which the
direction (tool face) of subsequent drilling tends to be in the
opposite direction (or nearly the opposite; depending, for example,
upon local formation characteristics) of the offset between the
tool axis and the borehole axis. The invention is not limited to
the mere use of a near-bit stabilizer. It is equally well suited
for "push-the-bit" steering in which there is no near-bit
stabilizer and the direction of subsequent drilling tends to be in
the same direction as the offset between the tool axis and borehole
axis.
[0028] The rotation of the drill string and the drilling force it
exerts are transmitted through the rotary steerable tool 100 to the
drill bit 32 by a rigid shaft 115. The shaft 115 is typically a
thick-walled, tubular member capable of withstanding the large
forces encountered in drilling situations. The tubular shaft 115
typically also includes a relatively small bore that is required to
allow flow of drilling fluid to the drill bit 32. Since the shaft
115 is rotationally coupled with the drill string and the housing
110 is substantially non-rotating with respect to the borehole, the
rotation rate of the shaft 115 relative to that of the housing has
been found to be a reliable indicator of drill string rotation. For
example, in one application using a "push-the-bit" configuration,
housing 110 was found to rotate one revolution every 2 or 3 hours
(a rotation rate of less than 0.01 rpm), while the shaft was
rotating at rate between about 100 and 200 rpm. Moreover, as
described in more detail below, measurement of the instantaneous
rotation rate of the shaft 115 has been found to be a reliable
indicator of stick/slip conditions during drilling.
[0029] FIGS. 3 and 5 show exemplary embodiments of sensor
arrangements deployed in the rotary steerable tool 100. A cross
section of one exemplary embodiment of sensor arrangement 200 is
shown in FIG. 3. Sensor arrangement 200 is also referred to as a
rotation rate measurement device. The sensor arrangement 200 is
disposed to measure the difference in rotation rates of the shaft
115 and the housing 110. In the exemplary embodiment shown on FIG.
3, sensor arrangement 200 includes one or more sensors 210 deployed
on an inner surface 112 of the housing 110. Sensor arrangement 200
further includes a plurality of markers 215 deployed in a ring
member 117 about the shaft 115. In use, sensor(s) 210 sends an
electrical pulse to a controller (described in more detail below)
each time one of the markers 215 rotates by the sensor 210. In the
exemplary embodiment shown, the controller receives three pulses
(one for each marker 215) per revolution of the shaft. It will be
appreciated that the invention is not limited in this regard and
that substantially any suitable number of markers 215 (one or more)
may be utilized. Furthermore, in alternative embodiments, the
sensor(s) may be deployed on the shaft 115 and the marker(s) may be
deployed on the housing 110.
[0030] In one advantageous embodiment, sensor 210 includes a
Hall-effect sensor and markers 215 are magnetic markers, although
the invention is not limited in this regard. Other sensor and
marker arrangements may be utilized. For example, in one
alternative embodiment, sensor arrangement 200 may include an
infrared sensor configured to sense a marker including, for
example, a mirror reflecting infrared radiation from a source
located near the sensor. In another alternative embodiment, sensor
arrangement 200 may include one or more ultrasonic receivers
(sensors) and ultrasonic transmitters (markers) deployed on the
shaft 215 and housing 210. In still another alternative embodiment,
sensor arrangement 200 may include one or more electrical switches
(sensors) and a plurality of cams (markers) disposed to open and
close the switches as they rotate past one another.
[0031] With reference now to FIG. 4, one exemplary method
embodiment 400 for quantifying stick/slip downhole in accordance
with the present invention is illustrated in flow chart form. A
rotary steerable tool (such as that shown on FIG. 2) is deployed in
a subterranean borehole at 402. As described above, the rotary
steerable tool includes a shaft that rotates in a substantially
non-rotating housing during drilling. At 404 the average and
instantaneous rotation rates of the shaft are measured as a
function of time, for example, as described below with respects to
Equations 1 and 2. At 406, the measured rotation rates are
processed to determine a stick/slip parameter. The stick/slip
parameter may then be transmitted to the surface at 408, for
example, using conventional telemetry techniques such as mud pulse
telemetry.
[0032] The rotation rates of the shaft 115 may be determined at
404, for example, by counting the number of sensed pulses in a
predetermined time period. This may be expressed mathematically,
for example, as follows:
R P M = N .DELTA. t 60 n Equation 1 ##EQU00001##
[0033] where RPM represents the rotation rate of the shaft 115 in
revolutions per minute, N represents the number of pulses recorded
in the predetermine time period, At represents the length of the
predetermined time period in seconds, and n represents the number
of magnetic markers utilized in sensor 200 (e.g., 3 as shown on
FIG. 4). An average rotation rate of the shaft may be determined by
counting pulses over a relatively long predetermined time period,
for example, from about 10 to about 60 seconds. To illustrate, if
75 pulses are sensed in a predetermined time period of 20 seconds
for a sensor arrangement having 3 markers, Equation 1 yields an
average rotation rate of 75 rpm. Instantaneous rotation rates may
be determined by counting pulses over relatively shorter
predetermined time periods, for example, from about 0.5 to 4
seconds. To illustrate further, if 10 pulses are sensed in a
predetermined time period of 1 second for the same sensor
arrangement, Equation 1 yields an instantaneous rotation rate of
200 rpm.
[0034] The rotation rates may also be determined at 404 from the
elapsed time interval between one or more pulses. This may be
expressed mathematically, for example, as follows:
R P M = 60 m n .delta. t Equation 2 ##EQU00002##
[0035] where RPM and n are as defined above in Equation 1 and
.delta.t represents the time interval between the m pulses in
seconds. Equation 2 may also be utilized to determine both
instantaneous and average rotation rates. To determine an
instantaneous rotation rate, m is typically in the range from about
1 to 10. To determine an average rotation rates, m is typically in
the range from about 50 to 200. To illustrate, an elapsed time
interval .delta.t of 0.1 second between sequential pulses (m=1) for
a sensor arrangement having 3 markers yields an instantaneous
rotation rate of 200 rpm. It will be appreciated that in moderate
to severe stick/slip conditions, the drill string (and therefore
shaft 215) can stop rotating for up to several seconds. In such
conditions it may be advantageous to set a predetermined maximum
elapsed time interval between sequential pulses. For example, if no
pulses are sensed for a whole second (a rotation rate of 20 rpm or
less in an embodiment having three markers), then the rotation rate
may be arbitrarily set to zero until the next pulse is received. It
will be appreciated that such an approach is consistent with
stick/slip conditions in which a drill string essentially stops
rotating for some period of time due to frictional forces and then
rotates rapidly for a short period of time during which the
torsional energy is released.
[0036] With continued reference to FIG. 4, a stick/slip parameter
may be quantified mathematically at 406, for example, as
follows:
S S N = R P M MAX - R P M MIN R P M AVE .apprxeq. R P M MAX R P M
AVE Equation 3 ##EQU00003##
[0037] where SSN represents a normalized stick/slip parameter,
RPM.sub.MAX and RPM.sub.MIN represent maximum and minimum
instantaneous rotation rates during some predetermined time period,
and RPM.sub.AVE represents the average rotation rate during the
predetermine time period (e.g., 20 seconds).
[0038] It will, of course, be appreciated that the stick/slip
parameter SS need not be normalized as shown in Equation 3, but may
instead be expressed as the difference between the maximum and
minimum instantaneous rotation rates as follows:
SS=RPM.sub.MAX-RPM.sub.MIN.about.RPM.sub.MAX Equation 4
[0039] In many applications, as described above, stick/slip
conditions cause the drill string to temporarily stop rotating
(i.e., RPM.sub.MIN=0). In such conditions, as shown in Equations 3
and 4, the stick/slip parameter is essentially equal to or
proportional to the maximum instantaneous rotation rate. As such,
it will be understood that RPM.sub.MAX may be a suitable
alternative metric for quantifying stick/slip conditions. Such an
alternative metric may be suitable for many applications,
especially since damage and wear to the drill bit, rotary steerable
tool, and other downhole tools is generally understood to be
related to the maximum instantaneous drill string rotation
rate.
[0040] It will, of course, be appreciated that the sensor pulses
need not be converted to rotation rates in order to determine the
stick/slip parameter. For example, SS and SSN may also be
equivalently expressed mathematically as follows:
S S = N MAX - N MIN .apprxeq. N MAX Equation 5 S S N = N MAX - N
MIN N AVE .apprxeq. N MAX N AVE Equation 6 ##EQU00004##
[0041] where SS and SSN are as defined above, N.sub.MIN and
N.sub.MAX represent the minimum and maximum number of pulses
recorded during a plurality of short duration time periods, and
N.sub.AVE represents the average number of pulses recorded in the
plurality of short time periods.
[0042] A suitable stick/slip parameter may also be determined by
differentiating the sensor pulses (e.g., the Hall-effect counts) or
the rotation rate of the shaft as a function time. For example,
stick/slip and/or normalized stick/slip parameters may
alternatively be expressed mathematically, for example, as
follows:
S S = ( R P M ( t ) ) t = R P M ( t ) - R P M ( t - 1 ) Equation 7
S S N = ( R P M ( t ) ) t R P M AVE = R P M ( t ) - R P M ( t - 1 )
R P M AVE Equation 8 ##EQU00005##
[0043] where SS and SSN represent stick/slip and normalized
stick/slip parameters, d(RPM(t))/dt represents the differential of
the instantaneous rotation rate with time, and RPM(t) and RPM(t-1)
represent instantaneous rotation rates of the shaft in sequential
time periods. It will be appreciated by those of ordinary skill in
the art that Equations 7 and 8 essentially determine the
variability of the rotation rate (or the instantaneous rotation
rate) with time. As described above, stick/slip conditions
typically result in a highly variable rotation rate. It will also
be appreciated, that such variability (and therefore a stick/slip
parameter) may be equivalently determined by differentiating (i)
the number of electrical pulses as a function of time or (ii) the
time interval .delta.t between pulses (or groups of pulses). It
will also be appreciated that the normalized stick/slip parameter
can be noisy when the average rotation rate is relatively small
(e.g., 10 RPM or less). To prevent false notification of severe
stick/slip (due to the measurement noise), the firmware may include
instructions, for example, to ignore normalized stick/slip
parameters when the average rotation rate is less than some
predetermined threshold.
[0044] Referring now to FIG. 5, one exemplary embodiment of sensor
arrangement 300 is shown in cross section. Sensor 300 includes a
sensor set 310 including a tri-axial arrangement of accelerometers
deployed in housing 110 of rotary steerable tool 100. In the
exemplary embodiment shown, x- and y-axis accelerometers are
aligned tangentially and radially, respectively, in housing 110,
although the invention is not limited in this regard. A z-axis
accelerometer will be understood to be aligned with the
longitudinal axis of the rotary steerable tool 100. Sensor
arrangement 300 may optionally include additional accelerometers,
for example, second x- and y-axis accelerometers diametrically
opposed from sensor set 310. Such additional accelerometers may
advantageously enable tangential and centripetal acceleration
components (e.g., due to stick/slip conditions) to be canceled
out.
[0045] Suitable accelerometers for use in sensor 300 are preferably
chosen from among commercially available devices known in the art.
For example, suitable accelerometers may include Part Number
979-0273-001 commercially available from Honeywell, and Part Number
JA-5H175-1 commercially available from Japan Aviation Electronics
Industry, Ltd. (JAE). Suitable accelerometers may alternatively
include micro-electro-mechanical systems (MEMS) solid-state
accelerometers, available, for example, from Analog Devices, Inc.
(Norwood, Mass.). Such MEMS accelerometers may be advantageous for
certain rotary steerable applications since they tend to be shock
resistant, high-temperature rated, and inexpensive.
[0046] The use of a tri-axial arrangement of accelerometers for
determining survey parameters, such as tool face and borehole
inclination, is known in the art. Since housing 110 is
substantially non-rotating with respect to the borehole, the x, y,
and z components of the gravitational field (measured by the
tri-axial arrangement of accelerometers) may be utilized to
determine gravity tool face and inclination of the rotary steerable
tool. This may be accomplished, for example, by averaging the
accelerometer measurements over a predetermined period of time
(e.g., from about 10 to about 60 seconds) to essentially average
out the effects of tool vibration and using the following known
equations:
G T F = arctan ( G X G Y ) Equation 9 Inc = arctan ( G X 2 + G Y 2
G Z ) = arccos ( G Z G X 2 + G Y 2 + G Z 2 ) .apprxeq. arccos ( G Z
) Equation 10 ##EQU00006##
. . . assuming {square root over
(G.sub.X.sup.2+G.sub.y.sup.2+G.sub.z.sup.2)} is approximately 1
G
[0047] where GTF represents the gravity tool face, Inc represents
the inclination, and G.sub.x, G.sub.y, and G.sub.z represent the
time-averaged x, y, and z components of the gravitational field. As
described in more detail below, sensor set 310 (including the
tri-axial arrangement of accelerometers) may also be advantageously
utilized to simultaneously determine axial (bit bounce) and lateral
vibration components during drilling.
[0048] With reference now to FIG. 6, another exemplary method
embodiment 500 in accordance with the present invention is
illustrated in flow chart form. A rotary steerable tool (such as
that shown on FIG. 2) is deployed in a subterranean borehole at
502. As described above, the rotary steerable tool includes a shaft
that rotates in a substantially non-rotating housing during
drilling. At 504, instantaneous and average rotation rates of the
shaft may be measured as described above. At 506, the rotation
rates are processed to determine a stick/slip parameter, for
example, as also described above. At 508, tri-axial acceleration
components of the rotary steerable tool housing 110 are measured.
At 510 and 512, respectively, the tri-axial acceleration components
are processed to substantially simultaneously determine inclination
and tool face and axial and lateral vibration components. The
stick/slip parameter and tool vibration components may then be
transmitted to the surface at 514, for example, using conventional
telemetry techniques such as mud pulse telemetry.
[0049] The accelerometer measurements are typically averaged over
relatively short time intervals (e.g., from about 0.1 to about 1
second intervals) to determine substantially instantaneous
tri-axial acceleration components. Tool vibration components (e.g.,
bit bounce and lateral vibration) may then be determined at 512
from the instantaneous acceleration components. It will be
appreciated that tool vibration components are typically determined
along each of the tool axes (x, y, and z). For example, a bit
bounce parameter may be determined from the z-axis (axial)
acceleration measurements and a lateral vibration parameter may be
determined from the x- and y-axis (cross-axial) acceleration
components. Tool vibration components may be determined
mathematically, for example, as follows:
T V = G i - G iAVE Equation 11 T V = G iMAX - G iMIN Equation 12 T
V = G iMAX - G iAVE Equation 13 T V = G iMIN - G iAVE Equation 14 T
V = ( G i ( t ) ) t = G i ( t ) - G i ( t - 1 ) Equation 15
##EQU00007##
[0050] where TV represents a tool vibration component (e.g., bit
bounce or a lateral vibration component), i represents one of the
x, y, or z axes such that G.sub.i represents an instantaneous
acceleration component along one of the x, y, or z axes, G.sub.iAVE
represents an average acceleration component over a relatively
longer period of time (e.g., from about 10 to 60 seconds to
determine the gravitational acceleration component), G.sub.iMAx and
G.sub.iMIN represent maximum and minimum instantaneous acceleration
components during a relatively longer period of time, and
G.sub.i(t) and G.sub.t(t-1) represent sequential instantaneous
acceleration components. It will, of course, be appreciated that
the tool vibration components determined in Equations 11-15 can
also be normalized, for example, as shown above with respect to the
stick/slip parameter in Equations 3 and 8.
[0051] While housing 110 (FIG. 2) is substantially non-rotating
during drilling (as described above), it can slip or rotate in the
borehole from time to time. This brief rotation may cause
centripetal and tangential acceleration of the housing, which, if
unaccounted, may be falsely attributed to a lateral vibration. Such
housing rotation may be accounted for through the use of additional
accelerometer deployments as described above. Alternatively,
rotation of the housing 110 may be detected via changes in the
gravity tool face. In the event that the change in tool face
exceeds a predetermined threshold (indicating excessive housing
rotation), lateral vibration may be ignored.
[0052] Exemplary method embodiments in accordance with this
invention advantageously enable downhole dynamics to be determined
using existing rotary steerable sensor deployments. Such methods
may therefore improve tool reliability as compared to prior art
dynamics measurement systems in that additional, dedicated sensor
deployments are not required. Moreover, the sensors (e.g., the
Hall-effect sensor and accelerometers) are all deployed in the
rotary steerable housing. Such deployment is also advantageously
very low in the BHA (i.e., close to the drill bit) and in close
proximity to sensitive rotary steerable electronics and hydraulics
components in the rotary steerable housing. It will be understood
that due to the mechanical coupling of the housing and shaft (e.g.,
via thrust bearings and bearing packs) vibration measurements made
in the housing, while not direct measurements of drill bit
vibration, are typically indicative of (e.g., proportional to)
vibration at the drill bit and elsewhere in the BHA.
[0053] With continued reference to FIG. 6 and reference again to
FIG. 4, downhole dynamics parameters (stick/slip, bit bounce, and
lateral vibration parameters) may be telemetered to the surface at
408 and 514 using substantially any known telemetry techniques. It
will be appreciated that it is typically desirable to telemeter the
dynamics parameter(s) in substantially real time so that corrective
measures can be implemented during drilling if necessary. Due to
the bandwidth constraints of conventional telemetry techniques
(e.g., mud pulse telemetry), each of the dynamics parameters is
typically reduced to a two-bit value (i.e., four levels; very low,
low, medium, and high). One exemplary encoding embodiment is shown
in Tables 1 and 2 (the invention is, of course, not limited in this
regard).
TABLE-US-00001 TABLE 1 Normalized Stick/Slip Parameter Normalized
Stick/Slip Level Binary Representation <50% Very Low 00 50 100%
Low 01 100 150% Medium 10 >150% High 11
TABLE-US-00002 TABLE 2 Bit Bounce and Lateral Vibration Bit
Bounce/Lateral Vibration Level Binary Representation <1 G Very
Low 00 1 2 G Low 01 2 3 G Medium 10 >3 G High 11
[0054] It will be understood that the telemetered dynamics
parameters may be advantageously used in combination with surface
indications of downhole dynamic conditions. For example, in shallow
wells, stick/slip is often manifest as a variation in surface
torque (or even a temporarily stalled drill string in severe
conditions). A driller may optionally compare and contrast surface
torque with the telemetered stick/slip parameter to obtain a more
complete understanding of downhole stick/slip conditions.
[0055] It will also be understood that the dynamics components
(stick/slip and tool vibration) may be advantageously saved to
downhole memory with much greater precision and frequency than they
can be telemetered to the surface (due to the constraints bandwidth
constraints of conventional telemetry techniques). This enables
analysis of the dynamics data after the rotary steerable tool has
been tripped out of the borehole (e.g., after completion of the
well). Such post-run analysis may be advantageously utilized for a
variety of purposes, for example, including improving the drill bit
and rotary steerable configurations and correlating tool wear and
failure with particular dynamics conditions. The saved dynamics
data may also be correlated with surface observations recorded in a
drilling log.
[0056] Referring now to FIG. 7, a block diagram of one exemplary
embodiment of a signal processing circuit 600 in accordance with
this invention is shown. It will be understood that signal
processing circuit 600 is configured for use with sensor
arrangements similar to those shown on FIGS. 2, 3, and 5, in which
a rotary steerable tool includes a rotation rate sensor and a
tri-axial arrangement of accelerometers. It will be further
understood that signal processing aspects of this invention are not
limited to use with sensors having any particular number of
accelerometers or rotation rate sensors. In the exemplary circuit
embodiment shown, accelerometers 601-603 are electrically coupled
to low-pass filters 611-613. The filters 611-613 may also function
to convert the accelerometer output from current signals to voltage
signals. The filtered voltage signals are coupled to an
Analog-to-Digital (A/D) converter 630 through multiplexer 620 such
that the output of the A/D converter 630 includes digital signals
representative of low-pass filtered accelerometer values. In one
exemplary embodiment, A/D converter 630 includes a 16-bit A/D
device, such as the AD7654 available from Analog Devices, Inc.
(Norwood, Mass.).
[0057] In the exemplary embodiment shown, A/D converter 630 is
electronically coupled to a digital processor 650, for example, via
a 16-bit bus. Substantially any suitable digital processor may be
utilized, for example, including an ADSP-2191M microprocessor,
available from Analog Devices, Inc. In the exemplary embodiment
shown, rotation rate sensor 200 (FIG. 1) is also electronically
coupled with digital processor 650.
[0058] It will be understood that while not shown in FIGS. 1, 2, 3,
and 5, rotary steerable tool embodiments of this invention
typically include an electronic controller. Such a controller
typically includes signal processing circuit 600 including digital
processor 650, A/D converter 630, and a processor readable memory
device 640 and/or a data storage device. The controller may also
include processor-readable or computer-readable program code
embodying logic, including instructions for continuously computing
instantaneous and average drill string rotation rates and a
stick/slip parameter therefrom. Such instructions may include, for
example, the algorithms set forth above in Equations 1 through 8.
The controller may further include instructions to receive
rotation-encoded commands from the surface and to cause the rotary
steerable tool 100 to execute such commands upon receipt. The
controller may further include instructions for computing gravity
tool face and borehole inclination, for example, as set forth above
in Equations 9 and 10, as well as tool vibration components as set
forth above in Equations 11 through 15. One skilled in the art will
also readily recognize that the above mentioned equations may also
be solved using hardware mechanisms (i.e., analog or digital
circuits). For example, the raw signal or the low-pass filtered
signal from the accelerometers could be AC-coupled to different
channels of the A/D converter. In this case, the mathematical
operation of Equation 11 (|G.sub.i-G.sub.AVE|), for example, may be
accomplished in the hardware (e.g., by removing a DC offset as
indicated).
[0059] A suitable controller typically includes a timer including,
for example, an incrementing counter, a decrementing time-out
counter, or a real-time clock. The controller may further include
multiple data storage devices, various sensors, other controllable
components, a power supply, and the like. The controller may also
include conventional receiving electronics, for receiving and
amplifying pulses from sensor 200. The controller may also
optionally communicate with other instruments in the drill string,
such as telemetry systems that communicate with the surface. It
will be appreciated that the controller is not necessarily located
in the rotary steerable tool 100, but may be disposed elsewhere in
the drill string in electronic communication therewith. Moreover,
one skilled in the art will readily recognize that the multiple
functions described above may be distributed among a number of
electronic devices (controllers).
[0060] Although the present invention and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alternations can be made herein without departing
from the spirit and scope of the invention as defined by the
appended claims.
* * * * *